In a rolling bearing, such as a ball bearing, a cylindrical roller bearing, a conical roller bearing, a self-aligning roller bearing, a needle bearing, and the like, used in an environment involving harsh lubrication conditions as in; for instance, an automobile, construction machinery, agricultural machinery, an iron and steel fixture, and the like, there is a high probability of: foreign substances being introduced into lubricating oil; indentation arising in a raceway surface as a result of biting of the foreign substances; and early exfoliation starting from the indentation.
A method proposed for solving the problem is to make an attempt to elongate flaking life by subjecting inner and outer rings and rolling elements to carburizing or carbonitriding, to thus precipitates a predetermined amount of retained austenite and relax the concentration of stress due to the indentation developed in the raceway surface (see Patent Document 1).
Another proposed method to make an attempt to extend the life is to enhance the hardness of a raceway surface by high-concentration carburizing, thereby enhancing the strength of a material (see Patent Document 2).
These methods are to strengthen individual components by taking the inner and outer rings and the rolling elements as individual components. Accordingly, when extension of life of the raceway ring is desired, an idea for subjecting a raceway ring to predetermined life-extending treatment is usually conceived.
Bearing steel typified by JIS SUJ2 or SUJ3 has hitherto been used for a rolling bearing, and the steel is usually used at hardness HRC 60 or more after having undergone quenching and tempering treatment.
However, in an environment where a foreign substance is contaminated to lubricant or insufficient lubrication is achieved as result of diversification of an environment where a rolling bearing is used, it may be the case where the bearing steel will fail to provide sufficient life or where seizure will arise. For these reasons, the steel is subjected to carbonitriding called marstressing, thereby making nitride into a solid solution and increasing the amount of retained austenite on the raceway surface. Thus, an attempt is made to relax the stress developed along an edge of the indentation in the foreign substances contaminated lubrication environment or enhance seizure resistance by an effect of nitrogen.
However, the environment where the rolling bearing is used has recently become harsh further, and there arises a case where a sufficient effect is not yielded by merely subjecting SUJ2 to carbonitriding. In order to solve the problem, a material provided with a large amount of added Si is used, and carbide or carbonitride containing Si and Mn is precipitated in an area percentage of 1 to 30%, thereby enhancing abrasion resistance and seizure resistance in an environment entailing occurrence of slide contact or an environment where lubricating oil becomes depleted. (see Patent Document 3).
Further, it has been well known that foreign substances, such as metal chips, shavings, burrs, dust resulting from abrasion, and the like, which are mixed in bearing lubricating oil inflict damage on a raceway ring or rolling elements of a rolling bearing, to thus significantly shorten the life of the rolling baring. Accordingly, the present inventor proposes that a content of C in the rolling surface layer of the bearing, the amount of retained austenite, and a content of carbonitride should be set to appropriate values even when the rolling bearing is used in the foreign substances contaminated lubrication environment, to thus relax the stress concentrated at an edge of indentation caused by the foreign substances, prevent occurrence of cracking, and extend the life of the rolling bearing (Patent Publication 1).    Patent Document 1: JP-A-64-55423    Patent Document 2: JP-A-7-41934    Patent Document 3: JP-A-2003-193200